structure. Even in high orbits, large quantities of propellants or sophisticated lightsailing techniques would have to be used to correct for the perturbing effects of solar radiation pressure. The scale of the effort required to deploy an orbital shade, especially one large enough to block the sunlight shining on a power satellite, would be large compared to the limited injury it would inflict. Since a shade would have to be lightweight to be worth deploying at all, it could be very easily removed from its original placement by any of the SPS's OTVs. Similar techniques might be imagined for blocking the microwave power beam from the power satellite to the ground. In this case, however, in order to block the beam full time, the microwave shade would have to remain in a 24-hour orbit at an altitude lower than the power satellite. At best, then, a series of microwave shades would have to be placed in circular trajectories around each power satellite in order to repeatedly eclipse its beam throughout its daily orbit around the Earth. Although microwave shades could be made of lightweight wire mesh and would thus experience little solar radiation pressure, the scale of effort required to deploy them would be greater than that required for the SPS owners to remove such shades. Nonexplosive projectile weapons were discussed briefly in Section 3. These would be particularly effective against targets in low Earth orbit where orbital speeds are highest, within reach of relatively simple sounding rockets. Dozens of nations and terrorist groups would be capable of fielding such rockets in the next few decades. In rather prosaic terms, a sounding rocket capable of reaching 477 km altitude (275 miles) could disperse 100 kg of 5-cm nails (about 6,000 nails) in a cloud with a radius of 35 meters in the path of the LEO base. With a closing speed of 11 km/sec (28,000 ft/sec), each nail with a mass of 16.5 gm would have a kinetic energy upon impact with the LEO base of 2 x 106 joules, equivalent to the explosive yield of 480 gm of TNT. (In contrast to TNT explosions, however, the kinetic energy of the nail is directed entirely along the relative velocity of the nail and the LEO base, so that the damage inflicted by each nail would be considerably greater than that due to 480 gm of TNT exploding against the hull of the LEO base.) In effect, the LEO base would be peppered with 1.6 hypervelocity bullets per square meter. Since flight time for the sounding rocket from liftoff on the ground to impact with the LEO base could be as little as 5 minutes, even an armed LEO base would have difficulty in destroying the rocket before it released its nails.
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